The challenge of radio frequency (RF) power amplifiers is to combine high efficiency, high bandwidth, high linearity, and high power. One potential architecture solution is the power digital-analog-converter (PowerDAC). The PowerDAC concept utilizes a digital data stream directly applied to the control of switching-power-amplifiers in a manner analogous to that of more conventional DAC circuits. In frequency ranges of multiple decades (VHF and UHF), and in a dynamic range fourteen bits or greater, conventional power amplifier technology and combiner techniques are inadequate.
The class-D power amplifier can operate efficiently through multiple decades of bandwidth. The class-D amplifier is a switching amplifier; therefore the voltage amplitude of its output is determined directly by its power supply voltage. Class-D amplifiers can suffer from high output resistance. OSISE is an optically-coupled, isolated, gate-drive circuit permitting fabrication of broadband class-D power amplifiers with high-side, floating-source switches, OSISE circuits are a significant development because they allow fabrication of broad-band totem pole, class-D half-bridges. Totem-pole architecture Class-D amplifiers are capable of producing RF power without output baluns or transformers.
Separate PowerDAC circuits may amplify individual bit streams. However, it is difficult to combine the output from separate PowerDACs. Separate signals require separate combining circuitry, which may require filtering and de-coupling. Combining analog conversions of digital signals is ineffective unless the amplification voltage is precise for each progressively less significant bit. Where PowerDAC circuits are separate, there may be no direct relation between the amplification voltages for each bit.
Consequently, it would be advantageous if an apparatus existed that is suitable for amplifying a digital signal and converting the digital signal to an analog signal without the use of separate combining circuitry.